1. Field of the Invention
The present invention relates to a control system of a semiconductor inspection system using a CD-measurement SEM or the like, or in particular to a control operation against the supply voltage drop.
2. Description of the Related Art
In the semiconductor inspection system using the CD-measurement SEM or the like, various disturbances including the mechanical vibration and the external magnetic field are liable to adversely affect the reliability of the inspection result. To cope with this problem, Japanese Patent No. 2911144 (Patent Document 1), for example, discloses a control method for automatically stopping the measurement whenever a mechanical vibration or an external magnetic field not smaller than a reference value is detected by a detection means.
The reliability of the inspection result is liable to be adversely affected also by the supply voltage drop as well as by the external disturbances. In the case where the supply voltage drops during the measurement, therefore, the reliability of the inspection result may be adversely affected. A supply voltage drop, however, poses not only the problem that the reliability of the inspection result is adversely affected but also the problem that the system itself may be shut down. This point is not dealt with by Patent Document 1.
To obviate the problem that the system itself may be shut down by the supply voltage drop, the conventional system uses an instantaneous voltage drop protector 17 as shown in FIG. 4. The instantaneous voltage drop protector 17 prevents the supply voltage applied to the system from being reduced and the system from being shut down by a supply voltage drop of a short duration. Also, the reliability of the inspection result is not adversely affected. The provision of the instantaneous voltage drop protector 17, however, leads to an increased system cost. In addition, the instantaneous voltage drop protector 17 has large footprints (installation space) and size, resulting in a bulky control system of a semiconductor inspection system.